The present invention relates to a method for driving an electrophoretic display which has dispersal systems comprised of pigment particles, a drive circuit for the display, and an electronic device in which the display is used.
Electrophoretic displays utilizing electrophoresis are classed as non-luminous devices. In electrophoresis, pigment particles migrate under the action of a Coulomb force which is generated when an electrostatic field is applied to a dielectric fluid in which the particles are dispersed.
In the conventional art, electrophoretic displays are known which consist of a pair of panels or substrates spaced apart in opposing relation, each of which is provided with an electrode. Between these electrodes a dyed dielectric fluid is provided. Differing voltages are applied via a switching element to the electrodes to generate an electrostatic field in the dielectric fluid, causing the electrically charged pigment particles to migrate in the direction of the applied field. Suspended in the fluid are particles having a pigment color different to the fluid in which they are suspended (hereinafter referred to simply as particles).
However, prior art electrophoretic displays suffer from a problem in that they afford poor viewing characteristics. The present invention has been made to overcome this problem, and provides for the first time an active matrix electrophoretic display, which display has superior viewing characteristics. As stated above, the object of the present invention is to provide an active matrix electrophoretic display. Also provided is a drive circuit integral to the device, and a method for driving the display by using the circuit.
The method of the present invention is applied to an electrophoretic display. The electrophoretic display comprises a first electrode, a plurality of second electrodes and a plurality of dispersal systems. The dispersal systems comprise a colored fluid in which pigment particles are suspended. A dispersal system is provided between the first electrode and each of one of the second electrodes. An electrostatic field is applied between the first and second electrodes for a predetermined time to cause the particles to migrate to a desired position corresponding to a color gradation of an image to be displayed.
In the method of the present invention, a constant voltage is applied for a set period of time which is calculated on the basis of a difference between a current average position of pigment particles and a subsequent desired position. By continually updating a voltage gradient using these position parameters, positions of pigment particles can be updated without the need for an initialization step. Since no initialization step is required, display updates can be affected rapidly. After applying the constant voltage to migrate particles to a desired position, the electrostatic field is removed and the particles become static, thereby providing desired display characteristics.
In the method and device of the present invention, to further improve display image characteristics, it is preferable for there to be variations in the properties of pigment particles employed. It should be further noted that when a voltage differential is cancelled between the 1st and a 2nd electrode by applying a constant voltage to make the pigment particles static, a capacitor formed by the 1st and 2nd electrode and the dispersal system functions to discharge an accumulated electric charge.
Furthermore, it is preferable before canceling a differential voltage between the electrodes to apply a differential voltage or brake voltage between the electrodes to brake movement of the particles. This is particularly important in the case that minimal fluid resistance acts against pigment particles, since, in such a case, there is significant inertial movement of particles and pronounced display fluctuations. This method enables to halt particles rapidly because the brake voltage is applied.
Since a direction of motion of a particle is determined by a direction of an applied electrostatic field, an applied brake voltage preferably has an opposite polarity to that of an initial voltage applied.
When applying a voltage between the 1st and 2nd electrodes, it is preferable that a time period for which the voltage is applied be measured against a reference time, so that in the event that the former time exceeds the latter, the voltage can be applied again, to prevent sedimentation or rising of pigment particles under gravity. In this way, display image characteristics provided by the method and device of the present invention can be maintained effectively.
A method of the present invention is employed in an electrophoretic display which comprises a plurality of data lines, a plurality of scanning lines each of which intersects each of the data lines, a common electrode, a plurality of pixel electrodes each of which is provided at each intersection spaced in opposing relation to the common electrode, a plurality of dispersal systems, each one of which comprises a colored fluid in which pigment particles are suspended, each of the systems being provided between the common electrode and one of the pixel electrodes, and a plurality of switching elements; with one of each of the switching elements being provided at a corresponding one of each of the intersections of the data lines and the scanning lines; with an on/off control terminal being connected to one of the scanning lines passing through one of the intersections; and with one of the data lines passing through one of the intersections, being connected to one of the pixel electrodes provided at each of one of the intersections.
The method comprises applying a predetermined common voltage to the first, common, electrode, selecting the scanning lines sequentially, applying a voltage during a predetermined time period to the selected scanning lines, to turn on all switching elements connected to the selected scanning lines, applying a constant voltage to each of the data lines for a set time period to migrate particles of each of corresponding pixels, and which are provided at the intersection of the data line and the selected scanning line, to attain a desired color gradation of an image to be displayed, and finally applying the common, first, voltage to the selected scanning lines.
It is to be noted that in the present invention, a constant voltage is applied as required, via switching elements, to respective pixel electrodes, over a set period of time, to attain a desired gradation of a displayed image. In addition, a common voltage is applied to the pixel electrodes to remove an electric charge accumulated between the electrodes, whereby an electrostatic field acting between the electrodes is removed, to fix a position of the particles, thereby creating a matrix in the electrophoretic display.
Furthermore, it is also possible to apply a brake voltage to a data line to brake particle motion before applying a common voltage to the data line, thus enabling particle movement to be halted rapidly. A method of the present invention is employed for an electrophoretic display which comprises a plurality of data lines, a plurality of scanning lines each of which intersects each of the data lines, a common electrode, a plurality of pixel electrodes each of which is provided at each intersection being spaced in opposing relation to the common electrode, a plurality of dispersal systems each one of which comprising a colored fluid in which pigment particles are suspended provided, each one of the systems being provided between the common electrode and one of the pixel electrodes, and a plurality of switching elements, with one of each of the switching elements being provided at a corresponding one of each of the intersections of the data lines and the scanning lines, with an on/off control terminal being connected to one of the scanning lines passing through one of the intersections; and with one of the data lines passing through one of the intersections, being connected to one of the pixel electrodes provided at each of one the intersections.further comprises applying a predetermined voltage to the first, common, electrode; applying a selection voltage to turn on all switching elements connected to a selected scanning line during a first period in one horizontal line scan; applying a constant voltage to data lines during the 1st period; and if a color gradation of a pixel to be displayed is not attained within a period during which the constant voltage is applied, selecting a scanning line corresponding to pixels in a 2nd period in the horizontal scan; and, further, applying the voltage to only a data line corresponding to the pixels in the second period.
In this invention, after applying the constant voltage to the pixel electrodes, the corresponding switching elements are turned off. The voltage applied is maintained as an accumulated charge between the electrodes. Once a set time period passes for attaining a desired color gradation of an image to be displayed, the switching elements are turned on again to apply the common voltage, and thus remove the electrostatic field acting between the electrodes. By using this method, a constant voltage can be applied over a longer period, and it is therefore possible to drive the data lines using a low voltage.
A method of the present invention is employed for an electrophoretic display which comprises a plurality of data lines, a plurality of scanning lines each of which intersects each of the data lines, a common electrode, a plurality of pixel electrodes each of which is provided at each intersection being spaced in opposing relation to the common electrode, a plurality of dispersal systems each one of which comprising a colored fluid in which pigment particles are suspended provided, each one of the systems being provided between the common electrode and one of the pixel electrodes, and a plurality of switching elements, with one of each of the switching elements being provided at a corresponding one of each of the intersections of the data lines and the scanning lines, with an on/off control terminal being connected to one of the scanning lines passing through one of the intersections; and with one of the data lines passing through one of the intersections, being connected to one of the pixel electrodes provided at each of one the intersections. The method comprising applying a predetermined voltage to the common electrode, applying a selection voltage to turn on all switching elements connected to the selected scanning line during a 1st period in a horizontal line scanning, applying a constant voltage to the data lines during the period, if a time to attain a color gradation of a pixel to be displayed passes after finishing applying the constant voltage, selecting the scanning line corresponding to the pixels during a 2nd period in the horizontal line scanning, applying the selection voltage to the selected scanning line, applying a brake voltage to brake a motion of the particles to only a selected data line corresponding to pixels in a selected period, and, after the particle movement is halted, selecting a scanning line corresponding to the pixels to apply the voltage to only the selected data line during a 3rd period of horizontal line scanning; and, finally, applying the common voltage to the data lines of pixel electrodes corresponding to pixels selected during the 3rd period.
Since, in the method of the present invention, it is possible to hold both the constant voltage and the brake voltage within one horizontal line scan, it is possible to lower not only an applied constant voltage, but also a brake voltage.
A drive circuit of the present invention is designed for use with an electrophoretic display, the drive circuit comprising a voltage application unit for applying a common voltage to the common electrode; a scanning line drive unit for selecting scanning lines sequentially, and applying a selection voltage to turn on all switching elements connected to those selected scanning lines; a data line drive unit for applying a constant voltage to respective data lines during a time period in which migration of particles of the pixel to a desired position can be effected to thereby attain a desired color gradation of an image to be displayed, and which applies the common voltage to the respective data lines.
In the present invention, a constant voltage is applied, as required, during a set period of time, via switching elements, to respective pixel electrodes to thereby attain a desired color gradation of a displayed image. Namely, by using the method and circuit of the present invention for driving an electrophoretic display, a matrix is created.
In addition, the common voltage is applied to the pixel electrode to remove an electric charge accumulated between the common electrode and the pixel electrodes after the switching elements are turned off, thereby removing an electrostatic field between the electrodes and fixing a position of the particles, to maintain a displayed image.
Furthermore, it is also possible to apply a brake voltage to each data line to brake particle motion after applying the constant voltage to the data lines, and before applying the common voltage to the data line, to halt particle movement rapidly.
A drive circuit of the present invention is utilized for an electrophoretic display and has a voltage application unit for applying a predetermined common voltage; a scanning drive unit which, during a 1st time period in each horizontal scan, selects scanning lines sequentially, by applying a selection voltage to turn on all switching elements connected to the selected scanning line, and when a time required for attaining a color gradation of a pixel to be displayed passes after finishing applying the selection voltage, selecting the scanning line corresponding to the pixel during a 2nd period of each horizontal line scanning, and applies the selection voltage to the selected scanning line; and a data line drive unit which applies the constant voltage to all the data lines during a 1 st period of each horizontal scan and applies the common voltage to the data line corresponding to the pixel.
It is also possible to utilize the drive circuit of the present invention in an electrophoretic display. The circuit includes a voltage applying unit for applying a predetermined common voltage, and a scanning drive unit. Each horizontal scan consists of a 1st, 2nd, and 3rd time period. In a first time period scanning lines are selected sequentially. Next, a selection voltage is applied to turn on all switching elements connected to the selected scanning line; and, when a time required for attaining a color gradation of a pixel to be displayed passes after selection of a scanning line in the 1st time period, a the scanning line corresponding to the pixel during the 2nd time period in a horizontal scan in which the scanning line is selected, and applies the selection voltage to the selected scanning line, selects the scanning line in the 3rd time period in a horizontal scan after a predetermined time passes; and a data line drive unit which applies the constant voltage to all the data lines during the 1st time period in a horizontal scanning, applies a brake voltage to stop the particles rapidly in the 2nd time period in which the scanning line is selected, and applies the common voltage to the respective data lines in the 3rd time period in which the scanning line is selected.
It is preferable that, when an displayed image is being switched, a time period used when migrating pigment particles in a pixel to a position to attain a color gradation of the pixel corresponds to a difference between color gradations both before and after switching.
An electronic device of this invention has a display unit utilizing electrophoretic display. For example, an electronic book, personal computer, mobile phone, electronic advertising board, and electronic traffic sign.